The use of molecular sieves for the separation of a component from a mixture of that component and several others is generally known. Further, crystalline aluminosilicates, generally referred to as zeolites, have been employed for the separation of a component from an aqueous medium, e.g. U.S. Pat. No. 4,014,711 discloses the separation of fructose from a mixture of sugars.
Zeolite-containing adsorbents are traditionally employed in separation processes in the form of agglomerates. The agglomerates have been traditionally formed using inorganic binders such as clays, silicas and alumina. The agglomerates are generally formed by extrusion into cylindrical or bead shaped particles which are thermally treated at elevated temperatures to set the binder. Some zeolites are not stable at the temperatures required for binding with use of such inorganic oxide binders and, accordingly, may not be formed with inorganic oxide binders.
Unfortunately, zeolites which have been bonded with inorganic oxides have been observed to deteriorate when employed for separations involving aqueous media. The degradation of the adsorbent results in contamination of the component being separated and the aqueous medium with the degradation products of the adsorbent. Further, the finite lifetime of the adsorbent necessarily requires more frequent replacement of the adsorbent for achievement of a desired separation.
The inherent problems associated with zeolite bonded with inorganic oxides may be alleviated by replacement of the inorganic oxide binder with an organic polymer binder.
Several organic polymer binders have been reported in recent years, e.g. see: U.S. Pat. Nos. 4,239,655, 4,248,737, 4,295,994, 4,298,501, 4,316,819, 4,319,928, 4,333,768, 4,333,769, 4,337,711 and 4,363,672. U.S. Pat. No. 4,239,655 discloses zeolite bodies produced from a mixture of zeolite, polycarboxylic acid and water. U.S. Pat. No. 4,248,737 discloses adsorbents formed by mixing together powders of an organic polymer binder and a liquid organic solvent. U.S. Pat. No. 4,295,994 is similar to U.S. Pat. No. 4,248,737 with the organic polymer binder being cellulose acetate. U.S. Pat. No. 4,298,501 is similar to U.S. Pat. No. 4,295,994 with the organic solvent being acetic acid. U.S. Pat. No. 4,363,672 is similar to U.S. Pat. No. 4,295,994 and relates to a separation process employing the compositions prepared in U.S. Pat. No. 4,295,994. U.S. Pat. No. 4,319,928 discloses a process for the separation of a component from a feed mixture comprising an aqueous solution of a mixture of components by use of an adsorbent comprising a clay bound crystalline aluminosilicate dispersed in an organic matrix, wherein the adsorbent is coated with a water permeable organic polymer. U.S. Pat. Nos. 4,333,768 and 4,333,769 discloses processes for separating feed components in an aqueous stream by use of the adsorbent compositions coated with a cellulose ether. U.S. Pat. No. 4,337,171 discloses an adsorbent composition comprising a mixture of zeolite X or zeolite Y, from about 5.0 wt. percent to about 35.0 wt. percent of an alkali or alkaline earth exchange resin and from about 20.0 wt. percent to about 35.0 wt. percent of a water permeable organic polymer binder, wherein the weight ratio of zeolite X or zeolite Y to the exchange resin is from about 1.0 to about 3. The organic polymer binder is disclosed to be cellulose esters such as cellulose acetate and cellulose nitrate. U.S. Pat. No. 4,316,819 relates to a process for preparing a crystalline aluminosilicate adsorbent wherein a mixture of aluminosilicate, powdered binder, water permeable organic polymer and a liquid organic solvent are formed into spheres prior to removal of the liquid organic solvent to form the final spheroidal adsorbent particles. The spheroidal adsorbent particles prepared by the process are also claimed.
The aforementioned patents relating to various organic polymer binders are similar in that in each the crystalline aluminosilicate and organic polymer binder are mixed together in the presence of an organic solvent. The organic polymer binder in such instances does not form a free-flowing latex as in the instant invention. The use of organic polymer and organic solvent tends to require a high level of organic polymer binder to provide sufficient binder strength. This increase in the amount of organic polymer binder results in a decrease in the performance of the adsorbent composition. For example, in Table 2 of U.S. Pat. No. 4,248,737 the separation of certain sugars is disclosed for adsorbents employing the organic polymer binder cellulose acetate or similar cellulose polymers and the adsorbents employ from 17.5 to 39.4 wt. percent of the cellulosic polymers in adsorbent compositions. The chromatographic tests in Table 2 show that the fructose retention volume is only 55% to 83% of that of an adsorbent formed with a binder of 20% clay. Thus, a reduction in retention volume and accordingly the efficiency of the adsorbent resulted from the effect of the cellulosic ester binders.
The instant invention overcomes the problems associated with the polymer bonded zeolites heretofore disclosed by employing latexes to prepare bonded crystalline molecular sieves, preferably aluminosilicates, i.e., zeolites, for use as adsorbent compositions. The use of latex binders results in adsorbent compositions having not only improved resistance to attrition, and binding strength but also having retention volumes which are often equal to or better then clay bonded adsorbents. Further, the instant invention minimizes the tendency of the polymer binder to block the pores of the molecular sieve and avoids the high temperatures of formation that are harmful to some molecular sieves.